Perforated plaster sound-deadening construction



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R. ERICSON Oct. 19, 1937.

PERFORATED PLASTER SOUND DEADENING CONSTRUCTION Filed Sept. 7, 1935 2 Sheets-Sheet 2 wie Patented Oct. 19, 1937 UNITED STATES PERFOBATED PLASTEB SOUND-DEADENING v CONSTRUCTION Application September 7, 1935, Serial No. 39,546

SCIaiml.

This invention pertains to betterments and improvements in the acoustical correction of rooms, auditoriums, and the like, and involves the use of perforations or apertures extending entirely through the wall surface, particularly of plaster construction, for the passage of sound waves into the interior region back of the outer surface where such waves are absorbed or dissipated by suitable means.

One object of the invention is to provide a sound-absorbing construction of high eillciency and one which at the same time will afford a surface which may be decorated in the usual way without interfering with the sound-deadening properties.

Another aim oi the invention is to ailord a procedure by which holes may be formed through the surface in situ, a further purpose of the invention being to supply a system of acoustical improvement which can be employed with most ordinary types of construction.

An additional object of the invention is to provide a material which may be applied like plaster and which will respond readily to the new and improved plan of acoustical betterment.

The present invention has the superiority over the prior art of giving the monolithic surface of an acoustical plaster, the comparative ease of application of an ordinary plastenthe avoidance of special attention to exterior painting, and the sound absorption is greater and the cost lower than those of the usual acoustical plaster material; or, stated somewhat otherwise, the new system of acoustical treatment affords the practical equivalent of tile insulation in the form of a plaster surface. Y

In practicing the present invention, a plastering base surface is used, a greater portion oi' which is capable of allowing the passage therethrough of a perforating instrument or tool, such as metal-lath, or any of the types of board commonly used as plaster base.

Over this surface a plaster mixture is applied which will bond to the base and which is capable of being decorated.

Holes or perforations are then made entirely through the plaster layer and the plaster base, allowing the sound waves to pass into the space back of the latter. f

In the space to the rear of the lath, means ar provided for absorbing or dissipating the sound waves, the most economical, eillcient, and convenient material for such purpose being freeflowing, granular, acoustical insulation, such as nodulated rock-wool, ground-cork, or exfoliatedvermiculite.

An important factor in this new process and construction is the plaster composition which has been found to be especially suitable for employ- (Cl. 'l2-17) ment in connection with this improved system oi' acoustical betterment.

Such plaster is composed preferably of one part by volume oi' gypsum plaster and two parts by volume of expanded or exfoliated vermiculite, but it has been found by experience to be advantageous to use a richer mixture for the base coat.

A plaster composition of this character has peculiar and noteworthy advantages for use in connection with the process and product of the present invention.

In the first place, because of the presence therein of expanded vermiculite, it has an appreciably greater degree of acoustical insulating power than does ordinary sand or gypsum plaster, but, secondly and of greater importance, it is of such a nature that after it has been placed on the walls in accordance with the usual plastering technique, it may be at any time thereafter conveniently and eillciently perforated by means suggested hereinafter, the peculiar adaptability to perforation being due to the unusual and marked physical characteristics of the expanded vermiculite which give to the plaster in which it is used in any appreciable quantity, and especially in proportions similar to those disclosed herein, properties of workability similar to those of wood, thus allowing it to be apertured or perforated with the customary drilling equipment, and it is, therefore, greatly superior to ordinary plaster in which sand is used instead of exfoliated vermiculite.

Such novel and improved vermiculite-plaster has three specific and outstanding points of superiority over ordinary sand-plaster, in that (a) it can be drilled without chipping of the edges or margins of the drilled holes, whereas the usual sand-plaster chips badly under the same conditions; (b) the structure is less abrasive than sand-plaster and the dulling of the drills therefore takes place much less quickly; and (c) because of the softer nature of the vermiculite-plaster considerably less power is required to drill it than for a similar operation in sand-plaster.

In order that those skilled in this art may readily understand the present invention and the advantages accruingfrom. its employment, in the accompanying drawings forming a part of this specification and to which reference should be had in connection with the following detailed description, several present preferred embodiments of the invention have been illustrated in detail, and to indicate clearly how the present new invention may be readily utilized to advantage examples of detailed methods of application will be resorted to.

In these drawings:-

Flgures 1 and 2 are fragmentary, perspective views of an embodiment of the invention employing expanded metal-lath as a base;

Figure 3 is a similar view showing the use of plaster-board as a base;

Figures 4, 5, 6, and 7 illustrate the manner 'of employing the invention in association with an old wall or ceiling;

Figures 8 and 9 illustrate the manner of using a fabric to prevent the sound-absorbing material from falling through the perforations of the plaster;

Figure 10 is an analogous view presenting the employment of a plastic paint:

Figures 11 and 12 show a convenient simple means for providing the perforations;

Figures 13 and 14 illustrate a multiple drilling mechanism; and

Figure 15 shows the use of a guide for positioning the drills during their aperture-forming operation.

Referring to these drawings, Figure 1 thereof shows how this invention may be carried out to advantage in the treatment of a ceiling for sound-absorbing purposes, and in this construction I I, I I are the usual ceiling-joists to which are applied sections or pieces of regular, Ndiamond-mesh, expanded-metal lath I2, and in making the joints in such lath, care should be exercised so that there are comparatively-wide openings in the diamond-shaped apertures where the sections of the lath overlap, this procedure being followed to permit good keys to form during the plastering operation and also to afford ease in penetration of the perforating tool.

A base-coat I3, desirably consisting of one part by volume of calcined-gypsum cement plaster and one part by volume of minus 8-mesh expanded vermiculite together with a suitable quantity of water, is applied to the lath in the usual manner and is permitted to set thoroughly and also t dry if desired.

On such base or scratch coat, a finish coat I4 of one part by volume of calcined-gypsum and two parts by Volume of exfoliated-vermiculite with a proper amount of water is applied and it can be left as a trowel finish, oated, or stipled.

p After such coat has set and before it has dried out, holes I of suitable size and properly spaced are punched through the plaster and the base, or the plaster may be allowed to dry and subsequently both coats may be drilled with the desired holes, these apertures allowing the sound waves to pass through into the region or space back of the coats where their energy is dissipated or absorbed.

Such holes are conveniently approximately .110 inch in diameter and are spaced Mg inch apart, but if the holes are drilled instead of vbeing punched out they may be made 1A inch in diameter and spaced 5/3 inch apart.

Some of the retaining keys of the plaster may be broken olf when these holes are punched or drilled, but a sufficient number of them will nevertheless remain to hold the plaster firmly in place.

These holes may be produced by any suitable and convenient type of punching or drilling tools or machines.

The sound-absorption capacity of such ceiling or wall may be increased by filling the space above or back of the holes with a sound-absorbing material, such asA plus 4-mesh exfoliatedvermiculite I6, although the perforated Vermittlaoe'aass lite-charged plaster alone provides sound-deadening system.v

'I'he same procedure may be followed for walls, in which case the added sound-absorbing material at the back of the wall is introduced from above. Y

In some instances, it may be found to be de,- sirable to suspend the rear sound-absorbing material a short distance above the perforated celling, such a construction enabling the sounddeadening medlum'to be applied in position before the plastering operation. Such a construction is shown in Figure 2, wherein a supplemental wire-mesh fabric2l supports the soundabsorbing material in the; manner indicated, the structure being otherwise as presented in Figure 1.

In both of these instances it may be expedient to use for the base coat a plaster material which is highly sound-absorbing whereby the portion of the plaster that forms the retaining keys may absorb and dissipate some of the sound energy which passes through the perforations.

In the modified construction of Figure 3, ordinary plaster-board lath base 3l is attached to the wooden ceiling-joists 32, 32, layers of plaster 33 and 34 being applied to this base in the usual manner but made from calcined-gypsum cement plaster and minus 8-mesh expanded vermiculite as presented above in connection withxthe constructions of Figuresjl and 2, and the surface of the plaster may be trowelled smooth, iloated, stippled, or other types of texture may be used.

The plaster can then be allowed to set and dry out, although the drying is not necessary, and then 1@finch holes 35 are drilled entirely through the plaster and plaster-board on s/-inch centers.

This construction will permit the sound-waves to pass through such wall or ceiling construction and into the region back of the plastered surface where some of their energy will be dissipated; however, in order to further increase the soundabsorption, fibrous, granular or other types of sound-dissipating material, preferably exfoliatedvermiculite 36, can be used in the space back of the plaster-board.

It is also possible to use this improved system conveniently and economically over old walls or ceilings in the manner shown in Figure 4, in which instance metal or wooden furring-strips 4I, 4I are attached to the surface of the old wall or ceiling 42 and to these strips plaster-board 43 is secured by nails or otherwise, and then the above-mentioned plaster 44 of calcined-gypsum and exfoliated-vermiculite is applied to such base. whereupon the holes 45 are drilled through the plaster and base inA the manner illustrated, a sound-absorbing agent 46, capable of being inserted between the furring-strips, being so introduced before the application of the plasterboard, such insulation-agent conveniently being in the form of a mat of rock-wool or balsam-wool, or, if preferred, this sound-dissipating medium 56, Figure 5, such as felt, may be secured directly to the back of the plaster-board before it is erected'and compressed somewhat at the furring-strips 5I, 5I when the plaster-board 53 is mounted in place.

InFigure 6 a modified construction is shown in which the sound-absorbing feltor its equivalent 66 is mounted on the surface of the old wall or ceiling before the placing of `the furring-strips 6I, 6I, plaster-board base 63 and plaster 64 are applied.

a A suitable Again, as illustrated in Figure '7, the felt 'I6 or 75 other sound-absorbing material may be cemented or otherwise attached to the old wall leaving a space between its surface and the adjacent face of the plaster-board 13.

In order to prevent any small quantity of dust or small particles of expanded vermiculite, rockwool, or other types of fibrous or granular material from falling through the holes into the room and becoming an annoyance, it is suggested that a fibrous membrane may be stretched back of the holes to hold the sound-absorbing material. The fabric can be of cotton (and if desired flre-proofed) of such a texture as to permit passage of sound and yet be tight enough to hold back the particles, this type of structure being presented in Figure 8 in which the membrane or cotton fabric is designated by the reference numeral 80. It is also feasible to stretch a porous fabric over the holes in front to mask them if they are objectionable; however, this may decrease the sound absorption somewhat, this arrangement being shown in Figure 9 in which the fabric is denominated 99.

All of the above-specified surfaces can be painted and decorated in the usual manner and this is considered as one of the advantages of this system of acoustical correction.

While I have used as my specific example an expanded-vermiculite plaster, I do not intend to limit my invention to this material because I may advantageously use other materials such as a plastic type of paint or other comparable spreadable material which may be applied to a wall suitably prepared as by the erection of a gypsum wall-board, but for obtaining the specific objects of the invention to the best advantage as applied to plaster, expanded-vermiculite plaster has been found to be preferable to any other material with which experiments have been made.

The employment of relatively thick plastic paint has been shown in Figure 10 in which construction the plaster-board base |0| is mounted on the joists |02 and on this the plastic paint |03 is applied with any style or type of texture desired, perforated v,metal tape |04 being secured. over the joints in the plaster-board to mask the cracks. The holes drilled through the paint and the plaster-'board have been designated |05 while the associated sound-absorbing medium has been characterized |06.

A single-punch type of apparatus incorporating an electric-motor which can be satisfactorily used for making the holes is shown in Figures 11 and 12, but a gang-drill like or similar to that shown in Figures 13 and 14 can be employed for making the holes at a much lower labor cost, as several holes can be drilled simultaneously.

In this gang-drill a housing III provided with handles |02, |32 encloses a plurality of inter- ,meshing gears III, |33, each of which meshes with the ones adjacent thereto in such a manner that they are all driven from a central flexibleshaft IM. Adjacent gears operate in opposite directions, and, accordingly, the drills |15, |35. of which .one is associated with each gear, are desirably right and left hand, depending on the direction of their rotation.

In order to provide a uniform spacing of holes, a drilling guide-strip |5|, such as is shown in Figure 15 is employed. This strip. preferably made of metal, has a single row of holes |52 properly spaced apart and countersunk so that one row of the drills shown in Figures 13 and 14 can be inserted therein for proper spacing of all the holes drilled out at that particular time. This guide-member or templet ISI has lugs |51, designed and adapted to be inserted in some of the holes already drilled for ease in properly placing and positioning the templet for use. When one course or set of holes has been completed, the guide or templet is moved over to the next position. If preferred, such templet or guide can be supported on adjustable posts |54 resting on and extended up from the floor.

While various plaster bases have been shown as specific examples, it should be understood that other plaster bases such as those incorporating organic fibre can be used in the same manner, and, in the case of bre boards as plaster bases, the perforations all the way through not only permit the sound to pass entirely through for absorption at the back surface but also afford absorption in the voids formed along the interior surfaces of the holes.

It will be obvious to those familiar with sound insulating materials that the effectiveness of the new system of acoustical treatment is in the penetration of the sound waves through the openings into the region back of the surface where the energy is dissipated in an absorbing material. It is possible to have some dissipation of the sound in this region without any sound absorbing material, depending upon the pitch. Such a system may be very successfully produced by the use of the vermiculite plaster perforated in situ as described above. However, the eillciency of the system may be improved by using a suitable sound-absorbing material in this space, and especially valuable results are obtained by the use of nodulated rock-wool, cork, exfoiiatedvermiculite, and the like.

In cases where dust may collect around the surface of the holes due to passage of air through the holes and the sound-absorbing material, such as a ceiling under an unfloored attic, the dirt collection may be decreased by sealing the space back of the sound-absorbing material to prevent this passage of air currents. It is possible, however, that the holes may be used for Ventilating purposes using a metal or glass wool over the holes to allow the passage of air. In this way, drafty movement of air caused by large ducts can be prevented and sound absorption is also obtained at the same time.

'I'he above examples are merely illustrative and are not intended to limit the scope of the invention as defined by the appended claims.

I claim:

1. In a wall construction, the combination of a base applied to said wall, an outer monolithic stratum supported by and covering said base, and a granular sound-absorbing material back of said base, said base and stratum having apertures extended entirely through both to allow passage of sound waves therethrough to the sound-absorbing material back of said base.

2. The wall construction presented in claim 1 in which the outer monolithic stratum is composed of a plaster incorporating expanded vermiculite.

3. The wall construction presented in claim 1 in which the outer monolithic stratum is composed of a plaster incorporating expanded vermiculite and in which the granular sound-absorbing material is expanded vermiculite.

RICHARD ERICSON. 

